The present invention relates generally to document scanners and, more specifically, to the mounting of spaced parallel mirrors therein to maintain precise spacing and parallelism of the mirrors while reducing the physical size of the scanner carriage.
Document scanners ordinarily employ a molded plastic housing in which the mirrors are positioned by referencing them directly to different parts of the plastic chassis, requiring the plastic chassis or housing to hold the tolerance. As is well known, it is difficult to hold a tight tolerance on an injection molded plastic chassis, especially under varying thermal conditions of use. Some past solutions have achieved the required tolerance by referencing the mirrors to each other through sheet metal plates, one on each end of the mirror. These plates are screwed onto the plastic chassis, and spring clips bias the mirrors to either end of the sheet metal plates. The plates also have bends which make the positional tolerances more difficult to achieve.
The mirrors in a scanner carriage housing must also maintain their exact parallel position and spacing despite any shocks during shipment or vibration during use which might be experienced. A very small translation or rotation in any of the mirrors may cause the scanner to lose its alignment. Accordingly, the mirrors must be tightly constrained to prevent such misalignment.
In the past, scanner mirrors have typically been biased and constrained to their datums by use of sheet metal spring clips pressing on the image plane side of the mirror. These clips require mirrors of extra length since a non-imaged surface of the mirror is occupied by the sheet metal spring clips.